Excessive Engine Knock L-48
Melting Slicks
Joined: Dec 2009
Posts: 3,229
Likes: 656
From: Thunder Bay
OK. Sorry. My mistake. Considering you changed the distributor, it's got to be a timing issue. sttocker31 is exactly correct with his assessment of how your timing should be set up. I like to set them up with about 14 degrees of initial advance with another 20-22 degrees of mechanical advance all in at around 3000 rpm. This gives a total mechanical advance of 34-36 degrees which is about right for a small block Chevy. Some engines like a little more, some a little less depending mostly on the head design. Vacuum advance should add another 12-16 degrees. The adjustments you have to work with are:
1) The stiffness of the mechanical advance springs which will control how quickly the advance comes in and what RPM it takes to get full advance.
2) The travel of the mechanical advance mechanism which controls how many degrees of advance you get with RPM and which is most often adjusted in aftermarket distributors by changing a bushing which travels in a slot.
3) The travel of the vacuum advance which controls how many degrees of vacuum advance you get. There are a couple of different vacuum advance limiters on the market. I think it's Crane that makes one that works on any distributor which is installed to limit the travel of the vacuum advance mechanism. MSD uses a cam (which is part of their vacuum advance) and can be turned to limit the travel. The disadvantage to the MSD design is that adjusting the vacuum advance travel changes the initial timing so you have to reset it with every adjustment.
4) The stiffness of the spring in the vacuum advance canister which is adjustable on many aftermarket vacuum cans with an Allen wrench and controls how much vacuum is required to activate the vacuum advance. Factory canisters are not adjustable.
5) And of course the initial timing setting.
You need a timing tape on your vibration damper or a dial-back timing light. Get some graph paper and a pencil and chart the curve you have now. Then you can figure out what you need to do to get the curve you need. Once you figure out how to do this and do it on a couple of your friends' cars, everyone will think you're a genius. Nothing makes power like setting up the advance curve correctly. Good luck.
1) The stiffness of the mechanical advance springs which will control how quickly the advance comes in and what RPM it takes to get full advance.
2) The travel of the mechanical advance mechanism which controls how many degrees of advance you get with RPM and which is most often adjusted in aftermarket distributors by changing a bushing which travels in a slot.
3) The travel of the vacuum advance which controls how many degrees of vacuum advance you get. There are a couple of different vacuum advance limiters on the market. I think it's Crane that makes one that works on any distributor which is installed to limit the travel of the vacuum advance mechanism. MSD uses a cam (which is part of their vacuum advance) and can be turned to limit the travel. The disadvantage to the MSD design is that adjusting the vacuum advance travel changes the initial timing so you have to reset it with every adjustment.
4) The stiffness of the spring in the vacuum advance canister which is adjustable on many aftermarket vacuum cans with an Allen wrench and controls how much vacuum is required to activate the vacuum advance. Factory canisters are not adjustable.
5) And of course the initial timing setting.
You need a timing tape on your vibration damper or a dial-back timing light. Get some graph paper and a pencil and chart the curve you have now. Then you can figure out what you need to do to get the curve you need. Once you figure out how to do this and do it on a couple of your friends' cars, everyone will think you're a genius. Nothing makes power like setting up the advance curve correctly. Good luck.
Is my vette stock?? HAHA
Joined: Oct 2015
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From: Im not allowed to tell you
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If you didnt check your timing before taking the distributor out you will need to verify your timing mark is still in the factory position. If your damper has rotated (either on the shaft or on the lamination between the steel and rubber ) and its no longer indicating tdc at 0, you will be chasing your tail trying to figure this out. Either get a TDC indicator or you will have to do some research on the other methods to do this.
Rough overview
https://www.hotrod.com/articles/accu...ne-piston-tdc/
Lots of different ways
https://dannysengineportal.com/top-d...t%20the%20stop.
Rough overview
https://www.hotrod.com/articles/accu...ne-piston-tdc/
Lots of different ways
https://dannysengineportal.com/top-d...t%20the%20stop.
Last edited by Rescue Rogers; Mar 26, 2021 at 08:03 AM.
Melting Slicks
Joined: Dec 2009
Posts: 3,229
Likes: 656
From: Thunder Bay
If you didnt check your timing before taking the distributor out you will need to verify your timing mark is still in the factory position. If your damper has rotated (either on the shaft or on the lamination between the steel and rubber ) and its no longer indicating tdc at 0, you will be chasing your tail trying to figure this out. Either get a TDC indicator or you will have to do some research on the other methods to do this.
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I have never experienced this personally so it doesn't usually come to mind, but you do have to make sure your timing marks are accurate, or all bets are off. There is also the possibility someone has installed the wrong timing tab and/or pointer so that your TDC mark is not correct. Verify TDC before you do any timing work.
